1. Field of the Disclosure
The present disclosure relates generally to an imaging device and is particularly directed to an intermediate transfer member (ITM) module of the type which controls the tension of the ITM belt of the ITM module within a predetermined range of tension.
2. Description of the Related Art
Toner transfer is a core process in an electrophotographic printing process. The process starts when a photosensitive roll, such as a photoconductor drum, is charged and then selectively discharged to create a charge image. The charge image is developed by a developer roll covered with charged toner of uniform thickness. This developed image then travels to what is referred to as “first transfer” in the case of a two step transfer system, or the only transfer process in the case of direct-to-paper systems.
In either system, the toner enters a transfer nip area between a photoconductor drum and a transfer roll. The media to which the developed toner image is to be transferred, either a transfer belt for a two step transfer system or a transport belt supporting paper for a direct-to-paper system, is positioned between these two rolls.
In a two step transfer system, the transfer belt, now carrying the charged toner, travels to a second transfer nip, similar in some ways to the first transfer nip. The toner is again brought into contact with the toner receiving medium in the second transfer nip formed by a number of rolls. Typically a conductive backup roll and a resistive transfer roll together form the two primary sides of the second transfer nip. Other designs include the use of two backup rolls disposed along the inside of the transfer belt for forming a wide second transfer nip.
For example, some printer architectures dispose the drive roll, which causes the transfer belt to rotate, between the first transfer nips and the second transfer nip. This allows first transfer to be isolated from nip shock effects of heavy media sheets entering second transfer and allows transfer belt tensioning in the web region where changes in belt length do not affect leading edge margins. In one such design, one of the two backup rolls which forms the second transfer nip is the drive roll.
Such a printer architecture is not without its shortcomings. The use of the drive roll as a backup roll at second transfer may result the in transfer belt wrapping less around the drive roll, thereby adversely affecting drive capability over the life of the transfer belt. Further, the transfer belt may tend to pull away from the media sheet at second transfer, thereby forming an air gap which results in an onset of transfer that occurs later than desired as well as premature Paschen breakdown, thus negating the benefit of a wide second transfer nip.